Re: [PATCH v8 3/4] fpga: dfl: add basic support for DFHv1

[matthew . gerlach]

On Fri, 30 Dec 2022, Xu Yilun wrote:

> On 2022-12-28 at 10:16:23 -0800, matthew.gerlach@xxxxxxxxxxxxxxx wrote:
> > From: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
> >
> > Version 1 of the Device Feature Header (DFH) definition adds
> > functionality to the DFL bus.
> >
> > A DFHv1 header may have one or more parameter blocks that
> > further describes the HW to SW.  Add support to the DFL bus
> > to parse the MSI-X parameter.
> >
> > The location of a feature's register set is explicitly
> > described in DFHv1 and can be relative to the base of the DFHv1
> > or an absolute address.  Parse the location and pass the information
> > to DFL driver.
> >
> > Signed-off-by: Matthew Gerlach <matthew.gerlach@xxxxxxxxxxxxxxx>
> > Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@xxxxxxxxxxxxxxx>
> > ---
> > v8: use struct_size() from overflow.h
> >     add dfh_get_u64_param_vals()
>
> Could you help check my comments?
> https://lore.kernel.org/linux-fpga/alpine.DEB.2.22.394.2212211421210.570436@rhweight-WRK1/T/#md86e3836130ebacd3c088f5c512ba741aac8a4d1


Sorry I missed your earlier comments. I have since responded to them 
specificially.


> [...]
>
> > +static u64 *find_param(u64 *params, resource_size_t max, int param_id)
> > +{
> > +	u64 *end = params + max / sizeof(u64);
> > +	u64 v, next;
> > +
> > +	while (params < end) {
> > +		v = *params;
> > +		if (param_id == FIELD_GET(DFHv1_PARAM_HDR_ID, v))
> > +			return params;
> > +
> > +		next = FIELD_GET(DFHv1_PARAM_HDR_NEXT_OFFSET, v);
> > +		params += next;
> > +		if (FIELD_GET(DFHv1_PARAM_HDR_NEXT_EOP, v))
> > +			break;
> > +	}
> > +
> > +	return NULL;
> > +}
> > +
> > +/**
> > + * dfh_find_param() - find parameter block for the given parameter id
> > + * @dfl_dev: dfl device
> > + * @param: id of dfl parameter
> > + *
> > + * Return: pointer to start of parameter block, NULL otherwise.
> > + */
> > +u64 *dfh_find_param(struct dfl_device *dfl_dev, int param_id)
> > +{
> > +	return find_param(dfl_dev->params, dfl_dev->param_size, param_id);
> > +}
> > +EXPORT_SYMBOL_GPL(dfh_find_param);
>
> Didn't find where to use it?

I understand. Don't export a function unless there is a comsumer for it.

> > +
> > +/**
> > + * dfh_get_u64_param_vals() - get array of u64 param values for given parameter id
>
> There is no rule to say one u64 for each property in the parameter block.
> So I don't see the reason for DFL core to provide u64 array for the API,
> And the size of the parameter block is decided by HW, why make the user
> input the value?
>
> As we discussed before, dfl core doesn't try to look into the parameter
> block. So please just provide the const void *data & data_size for drivers.
> This is the most common way to represent a data block.

I will move the parameter parsing helper function to the driver itself.

Thanks for the feedback,
Matthew Gerlach

> Thanks,
> Yilun
>
> > + * @dfl_dev: dfl device
> > + * @param: id of dfl parameter
> > + * @pval: location of parameter data destination
> > + * @nvals: number of u64 elements of parameter data
> > + *
> > + * Return: pointer to start of parameter block, PTR_ERR otherwise
> > + */
> > +u64 *dfh_get_u64_param_vals(struct dfl_device *dfl_dev, int param_id, u64 *pval, int nvals)
> > +{
> > +	u64 *param = find_param(dfl_dev->params, dfl_dev->param_size, param_id);
> > +	u64 next;
> > +	int i;
> > +
> > +	if (!param)
> > +		return ERR_PTR(-ENOENT);
> > +
> > +	next = FIELD_GET(DFHv1_PARAM_HDR_NEXT_OFFSET, *param);
> > +
> > +	if (nvals >= next)
> > +		return ERR_PTR(-ENOMEM);
> > +
> > +	for (i = 0; i < nvals; i++)
> > +		*pval++ = param[i + 1];
> > +
> > +	return param;
> > +}
> > +EXPORT_SYMBOL_GPL(dfh_get_u64_param_vals);
> > +